1. Field of the Invention
The present invention relates to the field of composite compounds of mineral or organic fillers or pigments containing at least two mineral or organic fillers or pigments of different natures and the uses thereof in the paper industry for manufacturing paper, for filling or coating purposes, or for any other surface treatment of the paper, as well as in the field of aqueous and non-aqueous paints and in the plastics industry.
2. Description of the Background
Composite pigments or fillers are commonly used these days for the manufacture of all types of paper, filling and coating or any other surface treatment of the paper in order to improve the quality of the paper in terms of its properties of opacity, whiteness and brightness of the sheets of paper, for example, or to improve the printability characteristics.
One widely used technique of producing composite pigments or fillers consists in mixing a mineral filler, such as a natural calcium carbonate for example, with a mineral filler such as talc (FR 2 526 061) or alternatively a mineral filler such as talc with another mineral filler such as calcined kaolin (EP 0 365 502).
Two other types of process are also known from the prior art for producing composite pigments or fillers meeting the requisite criteria for use in the paper industry.
A first category of these processes known from the prior art involves forming networks between the pigment particles, thereby creating numerous internal voids which then enhance the optical properties of the pigment fillers, often measured by a light scattering coefficient S.
Accordingly, patent WO 92/08755 describes a method of forming aggregates by flocculation and optionally by in situ precipitation of calcium carbonate, this flocculation occurring consecutively with the ionic interactions produced by using anionic polymers with a high molecular weight to flocculate the mineral particles to which multivalent cations such as the calcium ion are added on the surface.
Similarly, patent U.S. Pat. No. 5,449,402 discloses a product obtained by a method of creating internal voids based on ionic or electrostatic interactions, whilst U.S. Pat. No. 5,454,864 or U.S. Pat. No. 5,344,487 or EP 0 573 150 propose a composite pigment, the preparation of which is based on the attraction forces of ions.
These methods based on ionic attraction forces are sensitive to the ionic forces at play in the formulas used for paper coating colors or for paper filling and there is no guarantee that these pigments can be used in applications such as paper coating or paper filling.
A second category of these methods known from the prior art as a means of producing pigments with improved optical characteristics is based on using organic compounds of silicon (U.S. Pat. Nos. 4,818,294; 5,458,680) or chloride-based compounds (U.S. Pat. Nos. 4,820,554; 4,826,536; WO 97/24406).
Finally, a last known method of improving whiteness (WO 97/32934) consists in coating the pigment particles with another pigment particle such as very fine particles of precipitated calcium carbonate. However, a method of this type is not based on using an organic binding agent which creates a co-structure.
Faced with this problem of improving optical properties, such as opacity, whiteness, colouring or brightness, for example, or improving printability characteristics, the applicant has developed, for the- purposes of this invention, composite compounds, which are dry or non-aqueous or aqueous, of mineral or organic fillers or pigments which will improve at least one of the optical properties or printability required in the various fields of application, whilst providing a macroscopically homogeneous and stable compound in spite of the ionic forces present in the known formulas, such as offset or rotogravure paper coating colors or paper filling.